An extensive panel of monoclonal antibodies is being used to evaluate and characterize eosinophils in normal subjects and patients with eosinophilia resulting from infection or other causes. The data are being generated using a novel gating approach that was developed by Dr. Nutman's lab. These data are continuing to be collected for evidence of changes in peripheral eosinophils as a consequence of eosinophil mobilization and disease, in particular the hyper eosinophilia. They will be used to evaluate an extended pedigree with familial hyper eosinophilia.